1. Field of the Invention
The present invention relates to a ladder program retrieval device, and in particular to a ladder program retrieval device capable of retrieving a ladder circuit based on the operation conditions of specified signals.
2. Description of the Related Art
When creating a ladder program, verifying operation (debugging) and diagnosing abnormalities or the like during operation, associated ladder circuits are frequently called up onto a screen from a ladder program. Therefore, in many cases, functions for retrieving and extracting ladder circuits by setting, as a search condition, a signal and/or command used by the target ladder circuit are provided.
In general, when searching for a particular ladder circuit among a ladder program, a signal used by that ladder circuit is specified and the target ladder circuit is extracted by retrieving ladder circuits which include that signal. In general, the signal in the search condition is indicated by a text character string indicating a name (identifier), an address or the like assigned to that signal, and the search result is reported to an operator by calling up, onto a screen, the first ladder circuit that is determined to match the condition, or by displaying a list of all of the ladder circuits that are determined to match the condition.
For example, if a signal “A” is specified as a search condition in a ladder program editing device, and retrieval of ladder circuits is instructed on the basis of this search condition, then as in the search result 1 shown in FIG. 14, all of the ladder circuits in which the signal “A” appears are displayed as a list on the screen. When a retrieval method of this kind is used, as the ladder program becomes larger in scale, then a larger number of ladder circuits will match the same condition.
In this way, when multiple ladder circuits are listed on the display, it becomes more difficult to extract the target circuit, and ultimately, the operator is often required to visually check all of the ladder circuits that are displayed. However, when a large number of ladder circuits is displayed as a list of search results, it takes time to locate the target ladder circuit at a glance, and there is a high risk of the occurrence of errors, such as overlooking the circuit, or the like.
Therefore, a technique has been proposed conventionally wherein, by making it possible to set further detailed conditions in addition to the search condition, the number of ladder circuits determined to be matching is reduced and a target ladder circuit can be identified more accurately. For example, Japanese Patent Application Publication No. 2004-005060 discloses a control program retrieval device wherein a combination of commands and variables (signals) can be specified as search conditions. Furthermore, Japanese Patent Application Publication No. 62-086408 discloses a programmable controller wherein a sequence of commands and signals can be specified as search conditions. Moreover, Japanese Patent No. 4245811 discloses a ladder circuit editing device wherein search conditions can be specified by the ladder diagram pattern.
However, the problems indicated below occur when technology such as that disclosed in Japanese Patent Application No. 2004-005060, Japanese Patent Application No. 62-086408 or JP 4245811 is introduced. More specifically, in the case of ladder circuits, even circuits which have equivalent logic may differ in terms of the sequence of operation commands and/or signals, and since a junction which represents supplementary conditions may be inserted therein, then there is a risk of overlooking a ladder circuit that should be determined to be a match, if the matching is determined simply by a comparison of command sequences and/or ladder diagram patterns.